Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems facilitate increased productivity and cost reduction in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. Many of the electronic systems that provide these advantageous results often utilize reference currents in the performance of designated tasks. However, traditional precision reference current approaches are usually very expensive and often relatively limited.
A number of electronic components depend upon accurate reference currents to provide reliable results. Precision current references are often utilized in a variety of applications including precision delay stages, current sensing circuits for read paths in memories and timing circuits. However, maintaining relatively high accuracy and precision of such reference currents across process voltage and temperature (PVT) variations is usually very difficult and expensive.
Non-volatile memory macros with minimum area for embedded applications often utilize a reference current. These applications often use single ended memory bit cells instead of differential bit cells to conserve area. Relatively precise current references are utilized in the read sense path in order for such memory macros using single ended sensing schemes to have a fast read access along with good sense margin. These relatively precise current references are then used to design precision delay stages for use in the sense timing path or as a reference current to compare against in a current sensing scheme.
Traditional attempts at providing a precise current reference are usually expensive and often limited in precision. For example, given a zero temperature co-efficient (TC) voltage reference (e.g., a band gap reference), the classical way of getting a current reference is by designing a circuit that will give a current of Vref/R. In other traditional attempts, a current reference based on a proportional to absolute temperature (PTAT) voltage applied to a positive TC resistor (e.g., serial and parallel combination of resistors) is utilized. The resulting resistor should have the TC equal to the PTAT voltage (TCR=TCPTAT). Another convention attempt utilizes an Oguey's Current Reference (Ref: “CMOS Current Reference Without Resistance” by Henri J. Oguey, IEEE JSSC, vol. 32, No. 7, p. 573, July 1997). There are other current references based on Vt (e.g., threshold of MOSFET) where in the final current reference is given by Vt/R. The current references mentioned above usually require either special off-chip expensive resistors, are very sensitive to transistors mismatch or vary a lot across PVT.